1. Technical Field
The invention relates to a direct current (DC)-DC controller. Particularly, the invention relates to a DC-DC controller capable of dynamically adjusting an equivalent capacitance value.
2. Related Art
As shown in FIG. 1 and FIG. 2, a conventional direct current (DC)-DC converter 100 or 200 converts an input voltage VIN into an output voltage VOUT, and provides a load current ILOAD. A feedback voltage FB is extracted from the output voltage VOUT. The error amplifier 10 receives the feedback voltage FB and a reference voltage VREF to provide an error signal COMP. Then, the error amplifier 10 outputs the error signal COMP to a pulse width modulation (PWM) generation circuit 20. The PWM generation circuit 20 compares the error signal COMP with a ramp signal RAMP, so as to provide a PWM signal to an output stage 30.
When the load current ILOAD changes, the output voltage VOUT accordingly changes. The feedback voltage FB is processed by the error amplifier 10 to generate the error signal COMP. The error signal COMP and the ramp signal RMAP result in a long on-time period or short on-time period, until an average inductor current on an inductor LOUT is the same to the load current ILOAD, and the output voltage VOUT and the on-time period are recovered to an original level.
The DC-DC converter 100/200 includes a compensation unit 40A/40B. The compensation unit 40A is coupled between output terminal of the error amplifier and a ground terminal, and the compensation unit 40B is coupled between the output terminal and an inverting input terminal of the error amplifier. The compensation unit 40A or 40B includes a resistor R1 and a capacitance amplifying circuit 50. The compensation unit 40A or 40B is used to compensate the error signal COMP. However, an equivalent capacitance value of the capacitance amplifying circuit 50 is fixed, by which compensation of the error signal COMP cannot be speeded up when the load changes, so that a reaction rate in transient response cannot be improved.